Maternal body fat and water during pregnancy: Do they raise infant birth weight?

Objective: Our purpose was to determine the relation to infant birth weight of maternal fat and lean tissue during early and late pregnancy. Design: Total and net maternal pregnancy weight, fat, and water were determined from measurements of total body water, body density, and bone mineral mass in 200 women, with the use of a multicompartment model for body fat estimation in early and late pregnancy. Regression modeling was used to determine the relation of maternal body composition to birth weight, with control for maternal age, height, parity, and race and for infant gestational age and sex. Results: Maternal weight and body water at term were significantly associated with infant birth weight, but maternal body fat at term was not. These relations remained when maternal net values were used for weight, fat, and water to eliminate the contribution of the conceptus to these components. Conclusion: In well-nourished women delivering at term, maternal body fat near term does not contribute significantly to infant birth weight, but maternal body water does. (Am J Obstet Gynecol 1999;180:235-40)